# What infomation are needed to calculate fps for an air canon?

I know that fps is speed unit, and I'm trying to calculate the initial speed(or the power) for my air canon. Information I have: 1: value of the air chamber 2: psi 3: diameter of the barrel 4: length of the barrel 5: diameter of the air release valve will those information be enough? How to calculate fps or power from information above?

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8 years ago
O.K What you need is GGDT It is a program used to calculate statistics of air guns, here is a link:
GGDT
DesChamos8 years ago
Well, if its not yet built and you're trying to predict it, the math is going to be complicated.
However, if it's already built and you simply want to know, I'd suggest making a ballistics pendulum. I couldn't find any instructables on it, so here's something I found with a quick google: Ballistic Pendulum.
8 years ago
Also, page 147 of Backyard Ballistics by William Gurstelle.
you need a chronograph. To make the fps into mph, just divide fps by 1.47.
___8 years ago
just a guess but you might need some statistics of the projectile?
benthekahn8 years ago
The only way to get an accurate calculation is to find the amount of feet the projectile travels in a certain amount of time. The formula is Feet traveled/Amount of time. As an example, if the projectile traveled 200 feet in 2 seconds, it would be traveling at 100 fps. (200/2)
8 years ago
I think he mean calculate by the pressure. Since he want to know the fps before actually building the things up.
8 years ago
yeah, that would be hard to find though.